Japanese unexamined patent application publication No. JP-A-2000-250310 (Hereinafter, Patent document 1) describes a related art image forming apparatus. In the related image forming apparatuses such as electrophotographic printers, a photosensitive cartridge having a photosensitive drum is detachably mounted in an apparatus main body thereof, and a developing cartridge having a developing roller is detachably attached to the photosensitive cartridge.
In the photosensitive cartridge, there are formed receiving portions for receiving bearing units mounted at both end portions of the developing roller in such a state that the developing cartridge is attached thereto and guide grooves which are formed continuously to the receiving portions for guiding the bearing units to the receiving portions when the developing cartridge is attached thereto. In addition, by the developing cartridge being pushed into the photosensitive cartridge in such a manner that the developing roller approaches the photosensitive drum while the bearing units are being guided along the guide grooves, the attachment of the developing cartridge to the photosensitive cartridge is attained, whereby the developing roller is brought into press contact with the photosensitive drum.
A gear into which rotational force for rotating the developing roller is inputted is provided on the developing cartridge. In the configuration that has been described above, when rotational force is inputted into the gear, a rotational moment acting about the gear is generated in the developing cartridge, and the bearing units at both the end portions of the developing roller are pressed against the receiving portions in the photosensitive cartridge by the rotational moment so generated. In addition, since a force component acting in an attaching/detaching direction of the developing cartridge to/from the photosensitive cartridge is included in the force exerted on the receiving portions from the bearing units, the contact condition of the developing roller with the photosensitive drum can become unstable.
In addition, it is considered to suppress the deterioration (wear) of the developing roller that the developing roller is brought into contact with the photosensitive drum only when an image is formed while the developing roller is spaced apart from the photosensitive drum when no image is formed. When the developing roller is connected to or disconnected from the photosensitive drum in such a state that the photosensitive drum is rotating, if the developing roller is connected to or disconnected from the photosensitive drum after the developing roller has been stopped, the photosensitive drum is brought into sliding contact with the developing roller. Therefore, the developing roller is preferably spaced apart from the photosensitive drum while the developing roller kept rotating. In the configuration that has been described above, however, if the developing roller is connected to or disconnected from the photosensitive drum in such a state that the rotational force is inputted into the gear, since the component acting in the attaching/detaching direction of the developing cartridge to/from the photosensitive cartridge is included in the force exerted on the receiving portions from the bearing units by virtue of the rotational moment generated in the developing cartridge, the connecting/disconnecting operation of the developing roller can become unstable.